FIG. 13 is a block diagram which shows a conventional navigation device. In the figure, 101 is a map data base provided with polygon data for displaying buildings, roads or the like in 3D form. 102 is an overall operational control section which controls the overall operation of the device. 103 is an image generating section which generates images or the like for performing 3D display. 104 is an image display device.
The operation of the invention will now be explained.
The image generating section 103 searches for a map display range based on display viewpoint selection data and vehicle position data supplied through the overall operational control section 102. It reads road data and building polygon data and data for image display, performs conversion to a point coordinate system and perspective projection and generates an image for image display. A 3D map of fixed geographical points is displayed on the image display device 104 by the selection of display viewpoints.
Since conventional navigation devices are constructed as above, the problem has arisen that only the vicinity of the expressway is displayed in 3D form. Thus information related to the expressway is difficult to see and specific information with respect to normal roads other than the expressway can not be obtained.
The present invention is proposed to solve the above problems and provides a device which displays the contents of the expressway display in an easily understood way.